Feature request: Graceful cancellation of `follow_path` actions

[Rayman]

Feature request

Ability to let controllers handle cancelations gracefully

Feature description

At the moment when the follow_path action is cancelled, a zero velocity is immediately published (see the code and the figure below). We have a big heavy robot that needs a lot of time to slow down so we want to keep following the current path while decelerating within the deceleration limits.

With move base flex, we could override the cancel method and return when the cancellation was performed (see https://github.com/magazino/move_base_flex/issues/171) Is there a way to achieve this graceful cancel or can we add the same API to Navigation2?